Paul Pogba's Manchester United future continues to hang in the balance, with the Frenchman out of contract in the summer, and the Frenchman has declined to close the door on a Manchester City switch which would anger plenty of United fans.
While United remain hopeful of extending Pogba's stay at Old Trafford, he is believed to be open to joining another Premier League club, with City among those capable of meeting the World Cup winner's wage demands.
He would not be the first player to trade United for City, and not even the first to do so since the latter became power players in the Premier League, with Carlos Tevez making a notable switch back in 2009.
United and City is far from the only big footballing rivalry where such drama has unfolded, though. Here, Mirror Football looks at a selection of players who crossed some of the sport's biggest divides.
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Carlos Tevez
It wasn't just Tevez's move across the divide which hit a nerve - it was everything else that went along with it.
The infamous billboard took centre-stage, with the 'RIP Fergie' banner close behind, but to focus only on those matters is to ignore the changing tide between the two teams.
When Peter Schmeichel and Andrew Cole moved to City, they did so with their best days behind them, having achieved what they needed to do as United players.
Tevez, in contrast, had plenty left to give and was joining a team on the up, emphasising the fact when he played his part in City's dramatic late-season run to beat United to the 2011-12 Premier League title.
Sol Campbell
There are some Tottenham Hotspur fans who still haven't forgiven Campbell for his actions, more than 20 years after leaving the club for north London neighbours Arsenal.
Campbell had made his Spurs debut as a teenager and played more than 300 games for the club while establishing himself as an England international, but fear began to set in when it became clear he would be letting his contract run down in 2001.
Tottenham supporters began giving the defender a tough time more or less immediately, and it didn't stop after he retired, as events from last summer show.
"Are you going to keep worrying about me when I’m 80 years old?" Campbell asked in a talkSPORT documentary.
"I was 25 and now I’m 46. You’ve probably done things when you’re 25 or 15 or whatever. It doesn’t even make any sense now, move on.
Johan Cruyff
There are some players who you might expect to earn a new contract regardless of the stage of their career, and Johan Cruyff at Ajax was one of them.
The Dutch legend had returned to Amsterdam after spells in Spain and the United States, but opted to join rivals Feyenoord when the Rotterdam side were far from their best.
As author Andy Bollen put it for The Guardian, "Cruyff’s move to Feyenoord could be compared in the modern era to Lionel Messi signing for Real Madrid, or more realistically, in pure football terms, Mo Salah leaving Liverpool to sign for a struggling Manchester United, toiling around fifth or sixth, winning the league and cup double, and being named player of the year."
In Cruyff's final Ajax season, he won the league while Feyenoord finished a handful of points adrift, but the roles were reversed in 1983-84.
"He came to Feyenoord for revenge after they treated him badly at Ajax, his own team, and said OK I’m going to show you," Ruud Gullit would later say.
While Cruyff's past meant he would need to win over his new supporters, he did just that.
Mo Johnston
Mo Johnston didn't move directly from Celtic to Rangers, but the reaction meant he may as well have done.
After trading Parkhead for Ibrox via a spell in France with Nantes, the Glaswegian became a rarity - a Catholic footballer employed in the blue half of the city.
Johnston once said he would "walk over broken glass" to play for Celtic, and plenty of Rangers fans hadn't forgotten his allegiances by the time he joined the club in 1989 - especially given how close he was to rejoining Celtic before opting for a Gers switch.
“Hurting Celtic was not the drive behind the deal, but yes, I knew it would be a consequence," Rangers boss Graeme Souness would explain.
"I felt the manner of the move would damage them for a number of years."
Despite the move drawing Johnston hate from both sides of the divide - with Celtic fans dubbing him 'Judas' and a number of Rangers supporters unhappy with the signing themselves - the striker helped his new team win back-to-back league titles before departing for Everton.
Nick Barmby
Fans of Everton and Liverpool are often far from delighted when the divide is crossed, with the reaction to Rafa Benitez's arrival at Goodison Park over the summer just the latest major example.
It is perhaps unsurprising, then, that few big-money moves between the Merseyside rivals have taken place over the years.
The biggest fee paid from one of the clubs to the other is still the £6m spent by Liverpool when they brought England international Nick Barmby to Anfield in 2000.
“Gerard [Houllier] and Nick couldn’t be seen together. It was very cloak-and-dagger,” former Liverpool captain Jamie Carragher told The Athletic in 2020.
Everton chairman Bill Kenwright, meanwhile, has described the move as "the lowest of the low" for his time at the club.
"It was hearing he had used the six of the worst words in the English language as far as Everton fans are concerned," Kenwright explained.
"He had said: ‘I want to play for Liverpool’. To say I was shocked and surprised doesn’t begin to describe how I felt about it.”
Oscar Ruggeri
While plenty of players have turned out for both River Plate and Boca Juniors, few have prompted the reaction received by Ruggeri.
"I played for both River and Boca and I had a great time with both teams, but when I went from Boca to River they set fire to my house with my parents inside," former Argentina defender Ruggeri said in an interview with Marca.
"When they burned my house, I went to see the head of the Barras Bravas of Boca because he controlled everything and I told him it was the last thing I was going to put up with.
"Those guys ask you for things when you are a player and you are afraid because they threaten to do something to your family."
Now 60, the centre-back also enjoyed a spell with Real Madrid and had managerial stints with a number of clubs in his homeland and overseas, but neither River nor Boca or on that list.
Luis Figo
As far as European rivalries go, Real Madrid and Barcelona is right up there.
And while the atmosphere at your average Clasico might not always be as fierce as what we've seen at games between other huge rivals, the response after Luis Figo's move to the Bernabeu can hold a candle to pretty much anything else seen on a matchday.
"I came to Madrid to win more titles and for prestige. And on better financial terms, of course," the Portugal star would explain years after the move, but the financial aspect certainly felt like the bigger factor to Barca fans frustrated by the big-money departure.
When Figo lined up against his former club in 2002, a pig's head was thrown onto the pitch as he prepared to take a corner. That's certainly one way to show your dissatisfaction.
"The Barcelona fans adored Figo, and because they felt so close to him they couldn't understand how he could leave them in that way," former Barca president Joan Gaspart explained to the BBC.
"They conveyed this to him in their reaction in the stadium that night. To this day they still feel affected by it."
